In a conventional DC/DC converter shown in Patent Document 1, a high-voltage-side smoothing capacitor is connected in parallel to a series circuit having four switching elements (S1) to (S4) connected in series in this order via first to third connection portions, and a charge/discharge capacitor is connected between the first and third connection portions. Low-voltage-side voltage applied to the second connection portion via a reactor is stepped up through switching of the four switching elements (S1) to (S4) and then outputted from the series circuit. A first controller (25) calculates a first operation value on the basis of a difference between an output voltage target value Vout* and output voltage Vout, a second controller (26) calculates a second operation value on the basis of a difference between a charge/discharge capacitor voltage target value Vcf* and charge/discharge capacitor voltage Vcf, addition and subtraction of the first and second operation values are performed in control blocks (27), (28), and conduction rates for the switching elements (S1) to (S4) are controlled by gate signals G1, G2, to control output voltage and charge/discharge capacitor voltage, thereby preventing overvoltage breakdown of the switching elements (S1) to (S4).